The present invention relates to a construction for isolating the operator's seat in a crane cab from the normal vibrational, oscillatory and torsional movements to which the operator's cab is subjected.
By way of background, in the past overhead and gantry cranes used for ore bridges and the like included a girder structure made of steel lattice work which provided very little wind resistance and had great strength. Therefore, the trolley which was carried by the girder structure did not move in such a manner during operation so as to transmit extremely objectionable vibrational and oscillatory movement to the cab in which the crane operator was located. However, in recent years, box girders have replaced the lattice girders of prior cranes because box girders are less expensive. However, box girder bridge designs yield substantially lower natural frequencies of oscillation than lattice constructions. In many cases, this natural frequency is in the 2-10 Hertz range which causes discomfort to human beings. These natural frequencies are caused by the swaying and resonating of the box girder, so that the operator's cab, which is mounted on the trolley, is caused to vibrate and oscillate, much to the above-mentioned discomfort of the crane operator. The excitations causing these vibrations and oscillations include the wind, the trolley running over joints in the track on which it is mounted, the braking and accelerating of the trolley, and the twisting of the box girder. The present invention is directed to a construction for preventing the above-described vibrational and oscillatory movements from reaching the crane operator located in the cab.